Description

Qwen 3.5 don't think naturally on opencode.

Qwen 3.5 naturally have a long thinking chain with a specific structure that isn't present on opnecode.

I track the origin of this behavior to the next phrase of the default system prompt (packages/opencode/src/session/prompt/default.txt [line 14]): "Output text to communicate with the user; all text you output outside of tool use is displayed to the user."

Plugins

none

OpenCode version

1.2.24

Steps to reproduce

Extract this phrase from the system prompt and use in a simple chat, you will see the think chain shorter.

Screenshot and/or share link

Response to "hola" (hello in spanish) on Opencode

Response to "hola" (hello in spanish) on lm-sttudio with the system prompt

Natural Qwen 3.5 thinking (without this system prompt)

Operating System

Ubuntu 24.10

Terminal

No response